The Effect of a Rubber Sheet on the Dynamic Response of a Machine Foundation Located over a Small Thickness of Soil Layer

Placing a machine footing over a small thickness of soil layer, which is located over a bedrock, could encounter many challenges due to the bed’s notable stiffness in comparison to the soil. The advantages of using rubbers to protect facilities (structures, machine foundations, nearby footings and equipment, etc.) from vibration and control its consequences are well known nowadays. In this study, the benefits of employing a small thickness of rubber sheet (2 mm) on the dynamic response of a machine foundation which is located over four thicknesses of soil (210, 420, 630, and 840 mm) has been investigated. The soil layer is located over an artificial bedrock that is consisted of a thick concrete layer. The tests have been conducted in a vast test pit of size 2500×2500 mm and a depth of 840 mm by using a semi large-scale machine foundation model with a square concrete foundation of width 400×400×100 mm. It was observed that, by increasing the soil layer thickness, the resonant frequency and amplitude of the vibrating system decreases. Moreover, by employing a rubber sheet beneath the machine footing, the resonant frequency of the vibrating system significantly decreases especially for a small thickness of the soil layer. Although, using a rubber sheet could slightly increase the resonant amplitude, but the benefit of the resonant frequency-changing capability of the rubber sheet is too impressive by taking the resonant frequency of the system far enough from the unchangeable working frequency of the machine and preventing the resonant phenomenon to happen.

Study on dynamic characteristics of bio-inspired vibration isolation platform

Inspired by the body movement of the kangaroo, a multi-degree-of-freedom vibration isolation platform containing three units, that is, a protected object, a nonlinear energy sink, and an X-shaped structure, has been modeled, and the differential equations of the system have been given in the form of uniform relative coordinates. Furthermore, the displacement transmissibility analysis and numerical calculation are supported by the method of harmonic balance and Runge–Kutta algorithm, which shows that (a) there are nonlinear behaviors and resonant phenomenon in the time–frequency response and (b) quasi-periodic motion may be a predictor of periodic steady-state response or strong resonance, and the displacement evolution before quasi-periodic motion may be used to distinguish the two phenomena. In addition, based on the numerical method, the system energy changes in a selected frequency are discussed. Finally, the correctness of the theoretical analysis is verified by simulation data in Adams. Taken together, these results demonstrate that the dynamic characteristics are adjustable and designable of structural parameters in a specific frequency band and can provide a useful way to reduce the amplitude of resonant peaks and improve the vibration isolation performance for practical engineering applications.

Gamma oscillations in primate primary visual cortex are severely attenuated by small stimulus discontinuities

SummaryGamma oscillations have been hypothesized to play an important role in feature binding, based on the observation that continuous long bars induce stronger gamma in the visual cortex than bars with a small gap. Recently, many studies have shown that natural images, that have discontinuities in several low-level features, do not induce strong gamma oscillations, questioning their role in feature binding. However, the effect of different discontinuities on gamma has not been well studied. To address this, we recorded spikes and local field potential from two monkeys while they were shown gratings with discontinuities in space, orientation, phase or contrast. Gamma, but not spiking activity, drastically reduced with small discontinuities in all cases, suggesting that gamma could be a resonant phenomenon. An excitatory-inhibitory population model with stimulus-tuned recurrent inputs showed such resonant properties. Therefore, gamma could be a signature of excitation-inhibition balance, which gets disrupted due to discontinuities.

White nanolight source for optical nanoimaging

Nanolight sources, which are based on resonant excitation of plasmons near a sharp metallic nanostructure, have attracted tremendous interest in the vast research fields of optical nanoimaging. However, being a resonant phenomenon, this ideally works only for one wavelength that resonates with the plasmons. Multiple wavelengths of light in a broad range confined to one spot within a nanometric volume would be an interesting form of light, useful in numerous applications. Plasmon nanofocusing can generate a nanolight source through the propagation and adiabatic compressions of plasmons on a tapered metallic nanostructure, which is independent of wavelength, as it is based on the propagation, rather than resonance, of plasmons. Here, we report the generation of a white nanolight source spanning over the entire visible range through plasmon nanofocusing and demonstrate spectral bandgap nanoimaging of carbon nanotubes. Our experimental demonstration of the white nanolight source would stimulate diverse research fields toward next-generation nanophotonic technologies.

Static and Dynamic Magnetic Properties of FeGa/FeNi (FeNi/FeGa) Bilayer Structures

FeGa/FeNi bilayer structures with different deposition order were fabricated by the electrodeposition method on indium tin oxide (ITO) substrates. The structure, morphology, static and dynamic magnetic properties of FeGa/FeNi (FeNi/FeGa) films were investigated. The bilayer structures exhibit extremely various magnetic properties with different deposition order which could be attributed to the different coupling interaction in the interface. When FeGa is on top, the bilayer structures show lower coercivity than when FeNi is on top. Meanwhile, increase of the proportion of FeNi in the bilayer structure could affect the Hc and Mr/Ms. The ferromagnetic resonance peak of FeGa on top moves to a high field compared with FeNi on top. Moreover, FeGa on top shows improved complex permeability and a clear resonant phenomenon of the magnetization. These properties make FeGa/FeNi bilayer structure a potential candidate for high-frequency application.

MATRIX CAGES HOLDING SYSTEM FOR INDUSTRIAL FISH FARMING

In the paper, the technical aspects of modeling the retention system of matrixtype cages for industrial fish farming in a pond is considered. To date, there is no developed calculation methodology that takes into account the layout features of each cage module. The layout of the modules can vary significantly: from 1 to 36 cages of various designs. The aim of the work is to substantiate the parameters of the holding ropes, the length of the pull chains and the required mass of anchors by calculating the tensile forces in the ropes and the reaction of the anchor supports when solving the dynamic task in an unsteady setting. To solve this problem, a dynamic system was developed considering wind, wave, and inertial loads acting on all elements of the system: cage, holding ropes, chains, anchors. The force acting on the surface of the cage from the wind is received. The values of tensile forces in the ropes, the reaction of the supports of the anchors in three planes are obtained. The lengths of the chains are identified, ensuring the absence of tearing forces acting on the anchors. The masses of anchors are calculated taking into account the Archimedean force, depending on the density of the anchors’ material. The simulation lasted for 60 s. At 37 seconds of calculation, a resonant phenomenon was revealed: a significant increase in the breaking strength in the rope.

Acoustic metastructure for effective low-frequency acoustic energy harvesting

In this study, a multifunctional acoustic metastructure is proposed to achieve both effective low-frequency sound isolation and acoustic energy harvesting. A metallic substrate with proof mass is adopted to generate the local resonant phenomenon for the purpose of overcoming the drawbacks of the previous rubber film-based acoustic metastructure; the latter usually requires an elaborate tension process. Numerical simulations show that the proposed structure exhibits excellent noise isolation performance in the low-frequency band. Meanwhile, the incident sound energy can be converted into electrical energy with the help of an added piezoelectric patch. Numerical simulation results indicate that the harvested energy can reach the mW level. The parameters’ influence on the metastructure’s vibro-acoustic and energy harvesting performance are discussed in detail. An optimized configuration is selected and used for experimental study. It is demonstrated that 0.21 mW electrical power at 155 Hz can be harvested by the proposed metastructure under 114 dB sound pressure excitation.

Curvature instability of a curved Batchelor vortex

In this paper, we analyse the curvature instability of a curved Batchelor vortex. We consider this short-wavelength instability when the radius of curvature of the vortex centreline is large compared with the vortex core size. In this limit, the curvature instability can be interpreted as a resonant phenomenon. It results from the resonant coupling of two Kelvin modes of the underlying Batchelor vortex with the dipolar correction induced by curvature. The condition of resonance of the two modes is analysed in detail as a function of the axial jet strength of the Batchelor vortex. In contrast to the Rankine vortex, only a few configurations involving $m=0$ and $m=1$ modes are found to become the most unstable. The growth rate of the resonant configurations is systematically computed and used to determine the characteristics of the most unstable mode as a function of the curvature ratio, the Reynolds number and the axial flow parameter. The competition of the curvature instability with another short-wavelength instability, which was considered in a companion paper (Blanco-Rodríguez & Le Dizès, J. Fluid Mech., vol. 804, 2016, pp. 224–247), is analysed for a vortex ring. A numerical error found in this paper, which affects the relative strength of the elliptic instability, is also corrected. We show that the curvature instability becomes the dominant instability in large rings as soon as axial flow is present (vortex ring with swirl).